The present disclosure is directed to improved starch compositions, and methods of making and using the improved starch compositions. In particular, the disclosure is directed to starch compositions for use in papermaking processes, and to methods of preparing, manipulating and using the starch compositions during manufacture of paper products.
Numerous paper products are manufactured from fibers. These products are often manufactured from an aqueous slurry containing modified cellulose fibers derived from various plant sources. The slurry is formed in the wet end of a papermaking machine, where paper fiber is formed into a dilute water slurry and combined with a variety of materials before being distributed onto a paper machine wire. The water is subsequently removed from the slurry in a controlled manner to form a web, which is pressed and dried to create a finished paper product.
Additives can be incorporated into the slurry to enhance the papermaking process and to improve the finished papers"" aesthetic and functional properties. These additives can include starch compositions incorporated during the wet end of the papermaking process to improve drainage and retention, to add strength, and to improve formation properties of the paper. Starch compositions can increase ink penetration times, reduce lateral spread of printing inks, and improve imaging and contrast. Starch compositions can also increase the surface integrity of papers, thereby decreasing picking in uses such as printing and photocopying.
Other ingredients that can be incorporated into paper are microparticles, including specialty clays, silica, and other functional fine particles. These microparticles are often added during the wet end of the papermaking machine. Depending upon the type of paper being made, as well as the characteristics of the slurry, various different microparticles can be added. One of the challenges of using microparticles during papermaking is that the microparticles are not all retained on the web as the paper is formed. The microparticles that are not retained often end up being discharged, which can be expensive because the particles are not used. Therefore, it is desirable to enhance particle retention.
Drainage, or de-watering ability, is another important consideration in the manufacture of paper because it is related to how fast a paper machine can remove water from the web. Typically, improved dewatering corresponds to higher speeds on paper machines and to higher production rates of paper. Papermakers often seek to retain all fiber and particulates on the wire at the greatest speed economically possible, without sacrificing product quality. However, papermakers often experience drainage limitations while trying to maintain product quality, and therefore it is desirable to have high drainage values such that the paper can be made at high speeds and high quality.
Although papermakers and suppliers of paper ingredients realize that high retention and drainage are desirable, a considerable challenge in making consistent, high-quality paper has been that papermaking systems are not all alike and can show significant variation. This variation can be the result of changes in the ingredients in the paper furnish as well as variability in the papermaking equipment. These variations can make it difficult to produce quality paper at high speeds due to changes in particle retention and drainage.
Presently, most ingredients added to the papermaking slurry are optimized for use under specific conditions. This is true, for example, of starch compositions added to the wet end of the papermaking process. Unfortunately, conditions at most papermaking facilities vary over time as the ingredients and systems change. Therefore, a need exists for improvements that allow for satisfactory drainage and particle retention over a range of papermaking conditions.
The present disclosure relates to starches, for example cationic crosslinked starches, and to the use of those starches in papermaking. More particularly, the present disclosure is directed to starch and its use in wet end processing of a paper machine. The practices of the disclosure are particularly adapted for customization of the starch properties for specific wet end systems, and allow for modification of the starch properties to correspond to variations in the wet end of the papermaking machine.
The starch can also be modified during production by adjusting the starch functionality in the papermaking process. By selectively changing the crosslinking level of the starch, the drainage and retention properties of the paper furnish containing the starch are altered, which permits the starch properties to be tailored to provide improved performance depending upon the characteristics of the paper furnish in which it will be used.
The starch properties can further be adjusted immediately prior to use in the wet end of the papermaking machine in order to tailor the starch to the specific conditions existing in the papermaking machine. In this manner, the starch can be tailored to improve drainage and retention. This customization occurs, for example, by modification of the temperature at which the starch composition is cooked prior to addition to the wet end, by changing the period of time for cooking the starch, by changing the pressure at which the starch is cooked, and/or by changing the solids content of the starch prior to cooking. By adjusting these parameters, either individually or in concert, the properties of the starch are altered and can be conformed to specific conditions of various papermaking processes. For example, by cooking at higher or lower temperatures the starch properties are altered, and these altered properties can be used to improve wet end performance.
One implementation of the disclosure is a process for improving a papermaking method. The process comprises providing a papermaking furnish containing cellulosic fibers in an aqueous slurry to which is added a starch composition. The starch composition is typically a crosslinked cationic starch. The starch is cooked prior to addition to the papermaking furnish at a cooking temperature typically below 330xc2x0 F., and more typically from 180 to 250xc2x0 F., and even more typically less than 220 of or 230xc2x0 F. Such cooking temperatures are typically average cooking temperatures, which corresponds to the average temperature measured from two or more temperatures over time.
Microparticles, including nanoparticles, are also incorporated into the papermaking furnish to enhance machine performance, such as drainage and retention, and these microparticles typically have an average diameter of less than 1.0 micron, and more typically less than 0.1 microns. Suitable microparticles include, for example, various silica and clays.
The cationic crosslinked starch of the disclosure is typically mixed as a wet end additive into a paper furnish having a pH of from about 4.0 to about 9.0 in the wet end. The general manufacturing process for paper, including the term xe2x80x9cwet endxe2x80x9d, is described generally in Pulp and Paper Manufacture, Vol. III, Papermaking and Paperboard Making, R. G. McDonald, editor, J. N. Franklin, tech. editor, McGraw Hill Book Co., 1970.
In specific implementations, the starch and methods are used to improve dewatering of papermaking furnishes. As the furnish is dewatered during the papermaking process, the dewatering rate is evaluated. If this dewatering rate is unsatisfactory, then the cooking temperature of the starch is modified in order to alter the dewatering properties. The modification of the cooking temperature should be sufficient to produce a modification in the dewatering or first pass retention of the papermaking furnish. Typically, the amount of modification in the temperature is greater than 1xc2x0 F., and more typically at least 5xc2x0 F. In specific implementations, the amount is from 5 to 10xc2x0 F. In certain implementations the modification is at least about 10xc2x0 F. The temperature is increased in certain implementations, and decreased in other implementations, depending upon the dewatering or drainage performance prior to modification of the cooking temperature.
It is sometimes necessary to determine the proper change in temperature through iterative changes in temperature followed by evaluation of the paper properties. Such iterative changes allow for step-wise evaluation and adjustment of the furnish properties. For example, when dewatering properties are unsatisfactory or show deterioration, the temperature can be initially lowered by a specific temperature (for example, 5xc2x0 F). If this lowering shows improvement in dewatering, then the temperature can be maintained at this new temperature. Alternatively, the temperature can be further lowered to seek even At greater improvements in dewatering levels. If this lower temperature improves the dewatering properties, then the temperature can be kept at this level (or lowered further to seek even greater improvements). However, if this lower temperature does not improve the dewatering properties, then the temperature can be raised back to the previous level. Alternatively, the temperature can be raised part way back to the previous level.
If the initial lowering does not result in an improvement in the dewatering properties, then the temperature should typically be raised above the initial temperature to determine if the dewatering properties improve. If the dewatering properties do not improve, then the temperature should be returned to the initial temperature or returned to a temperature intermediate the initial temperature and the raised temperature. If the dewatering properties do improve, then the temperature can be maintained at the heightened temperature or raised again to seek an even greater temperature. In this manner and similar manners the temperature at which the starch is cooked is used to alter the properties of the starch produced, thereby tailoring those properties to the wet-end properties of a paper machine. In addition to adjusting the retention and drainage properties by adjusting the cooking temperature of the starch, these properties can be adjusted by modification of the pressure at which the starch is cooked and by changing the solids content of the starch prior to being cooked. For example, the starch is typically cooked in a jet cooker at a pressure of less than 100 pounds per square inch; and the starch is typically added to the jet cooker at a solids content of less than 10 percent. By altering the pressure or the solids content, the starch composition can be tailored to the specific properties of the wet end furnish to which they are added.
Not only can the temperature, pressure, and solids levels be independently modified to improve the wet end performance, but they can be modified together to change the starch properties. For example, all three parameters can be changed, the temperature and pressure can be changed, the temperature and solids content can be changed, or the pressure and solids content can be changed. Also, besides drainage and retention, other improvements can be made in the wet end properties, such as improvements in line speed that are often observed along with improvements in drainage and retention.
A further implementation includes a process for adjusting a papermaking method. The process entails adjusting the temperature at which the starch composition is cooked in order to obtain improved drainage or retention properties of the papermaking furnish. The process includes providing a papermaking furnish containing cellulosic fibers and microparticles in an aqueous slurry, and providing a starch composition formulated for addition to the papermaking furnish. A portion of the starch composition is cooked at an initial temperature and then added to the papermaking furnish. The furnish is subsequently dewatered to form a cellulosic fiber web. An assessment regarding the rate of dewatering or particle retention of the aqueous slurry is made, and if the dewatering is at an unsatisfactory rate then the temperature at which the starch composition is cooked is changed to a different temperature in order to modify the rate of dewatering of the aqueous slurry.
The above summary of the present disclosure is not intended to describe each embodiment of the present disclosure. This is the purpose of the figures and the detailed description which follow.